2MarcinW
Then I suggest:
13.04.18 Fixed: Copying to t:\ fails if it is a drive made with the subst command for dirs with write access for which SetCurrentDirectory didn't work...
or:
13.04.18 Fixed: Copying to t:\ fails if it's subst'ed drive for dirs with write access for which SetCurrentDirectory didn't work...

On MSDN Microsoft writes is as this: SUBSTed

Subst'ed or SUBSTed indicates a constructed word - substed doesn't - and substed is not an ordinary English word.

You got a point - on the other hand "dir" and "subdir" are used a lot of places in TC's dialogs, substed is not. So TC users are familiar with dir and subdir, but not necessarily with subst and substed. But then again, you can argue that people (geeks ) who read history.txt files most likely will understand what substed means.